1. Field of the Invention
The present invention relates to a scanning tunnel-current-detecting device comprising a mechanism for canceling variations caused by thermal drifts and mechanical vibration, and a method for detecting a tunnel current and to a scanning tunnelling microscope and a recording/reproducing device utilizing a method for detecting tunnel current.
2. Related Background Art
Recently a scanning tunnelling microscope (hereinafter referred to as STM) has been developed [G. Binnig et al., Helvetica Physica Acta, 55, 726 (1982)] which enables direct observation of electronic structure of the atoms on the surface of a conductor, and allows a measurement of an image of real space of not only a single crystal but also an amorphous material with high resolution. This measurement has an advantage that an observation can be made with low electric power without impairing a medium by a current. Moreover, this measurement can be conducted in an atmospheric environment and is applicable to various materials, so that the method is promising in a variety of technical applications.
The STM utilizes a tunnel current which flows between a metallic probe (or a probe electrode) and an electroconductive material (or a sample) when an electric voltage is applied therebetween and the both are brought into proximity as close as approximately 1 nm to each other. This current is extremely sensitive to the change of the distance between the probe electrode and the sample, so that the scanning with a probe at a constant tunnel current allows depiction of the surface structure of the real space and simultaneously gives various informations regarding the whole electronic clouds of surface atoms.
To the STM for this purpose, a vibration isolator is indispensable which reduces external disturbances caused by floor vibration, and a minute deformation of constituting material caused by ambient temperature variation to less than a resolution limit.
Generally, for eliminating the influence of vibration, passive measures are taken such as a method of reducing vibration by dissipating a vibration energy with a damper element of a dynamic vibration isolator, and a method of lowering resonance frequency by employing a relatively massive body as the supporter or the stand to increase a resistance to vibration.
Not so serious problem is encountered thereby in observation of a local atomic arrangement of a sample by locally scanning a probe electrode of STM. However, in observation of the surface state of a sample over a relatively large area by scanning a probe electrode of STM for a long time, there arises a problem that an influence of temperature drift caused by a thermal contraction or expansion of the member constituting STM and the sample to be measured become significant, and lowering the measurement precision ensues. The variation caused by the temperature drift may sometimes reach approximately 0.5 .mu.m (in the Z direction).